Colony stimulating factor-1 (CSF-1) is the primary growth factor regulating macrophage survival, proliferation and differentiation as well as morphology, adhesion and motility. CSF-1 regulation of macrophages plays an important role in enhancing the progression and metastasis of solid tumors. CSF-1 expression and the presence of tumor-associated macrophages (TAMs) in human breast cancer are correlated with poor prognosis. Mammary tumor metastases are severely reduced in the macrophage-depleted CSF-1-deficient (Csf-1op/Csf-1op) mouse. Furthermore, in mouse models of breast cancer, TAMs, angiogenesis, metastasis and intravasation can be reduced and the life of tumor bearing mice prolonged by removing CSF-1, or blocking the CSF-1 R. Previous studies of this Program have demonstrated the existence of a paracrine interaction between TAMs and carcinoma cells necessary for the promotion of invasion of mammary tumor cells in mice and suggest that CSF-1 exerts these effects by regulating macrophage chemotaxis and the secretion of angiogenic and tumor cell chemotactic factors. In this project it is proposed to study the molecular mechanisms of signaling from the CSF-1 receptor that regulate these processes. The rationale for the proposed studies is that an understanding of the molecular mechanisms involved will provide novel therapeutic targets in breast cancer. Preliminary experiments indicate that the signaling pathways downstream of CSF-1 R Y721 and Y706 phosphorylation, respectively positively and negatively regulate macrophage motility and tumor cell invasion in vitro. The overall aim of the proposal is to elucidate the signaling pathways that regulate macrophage motility and tumor cell invasion and to identify the angiogenic and tumor cell chemotactic factors produced by macrophages and to evaluate their significance for tumor progression and metastasis. The specific aims are: Aim 1: To define CSF-1 receptor pY721-based signaling pathways that enhance macrophage chemotaxis. Aim 2: To identify the tumor cell chemotactic and angiogenic factors synthesized and secreted by macrophages and the CSF-1 R phosphotyrosine signaling pathways regulating their production. Aim 3: To determine the significance of identified CSF-1 chemotactic signaling pathways and macrophage tumor cell chemotactic and angiogenic factors in tumor progression and metastasis. Relevance to public health: Breast cancer is the leading cancer of women. Previous studies have shown that particular non-tumor cells (TAMs) in the tumor microenvironment enhance tumor progression and metastasis. This project focuses on identifying the underlying mechanisms of this enhancement with the goal of identifying novel therapeutic targets.